In the past, as an electrophotographic image-forming apparatus using an intermediate transfer belt, the following is known. A toner image formed on a photoreceptor is transferred onto an intermediate transfer belt, and then, the toner image on the intermediate transfer belt is transferred to a transfer material such as transfer paper (recording paper). That is, after primary transfer of a toner image charged on a predetermined polarity formed on a photoreceptor to an intermediate transfer belt, the toner image on the intermediate transfer belt is secondarily transferred onto a transfer material using electrostatic force.
An image-forming apparatus using such an intermediate transfer belt sequentially superimposes toner images formed on each photoreceptor on an intermediate transfer belt by utilizing electrostatic force. Further, it is possible to collectively transfer the superimposed toner images to the transfer material. Therefore, it is widely used as a color image-forming apparatus.
In recent electrophotographic image-forming apparatuses, various transfer materials are used, and not only plain paper and OA exclusive paper but also thick paper or coated paper, and paper having irregularities on the surface (hereinafter also referred to as “uneven paper”) are required to handle as a paper type. Particularly, embossed uneven paper on its surface is increasingly used for business cards and for a cover of printed matter from its unique texture.
However, it is known that uneven papers are inferior in transferability as compared with other smooth papers, and it is difficult to satisfactorily form images thereon. Various studies have been made in order to improve uneven paper transferability.
For example, by using an elastic belt, it is possible to improve transferability by deforming the belt along the surface shape of the uneven paper. However, when the belt is stretched and contracted during transfer, there is produced a problem that the belt deteriorates due to prolonged use and cracks.
In order to increase the transferability, it is conceivable to strengthen the transfer electric field acting on the toner. However, when the applied voltage at the time of transfer is increased in order to strengthen the transfer electric field, image noise due to discharge occurs. As a method of increasing the transfer electric field to the toner with the same applied voltage, it has been studied to lower the volume resistivity of the intermediate transfer belt or increase the relative dielectric constant of the intermediate transfer belt (refer to Patent Documents 1 and 2: JP-A 2000-231289 and JP-A 08-152759).
However, when the relative dielectric constant of the intermediate transfer belt is increased in order to increase the transfer electric field acting on the toner, the image force of the intermediate transfer belt and the toner is increased by the dielectric polarization. This is disadvantageous for secondary transfer of the toner from the intermediate transfer belt to the transfer material. In addition, when a filter having a high dielectric constant (it may be called as a high dielectric filler) is added, durability deteriorates, such as cracking at the interface, therefore and intermediate transfer belt excellent in uneven paper transferability and durability has been desired.